The present invention relates to the preparation of symmetrical tetrachloropyridine, i.e., 2,3,5,6-tetrachloropyridine, hereinafter referred to as "sym-tet", from chlorinated .beta.-(trichloromethyl-)pyridines in a catalyzed reaction.
Sym-tet is a well known compound useful as a chemical intermediate in the preparation of a variety of pesticides. Previous methods for preparing sym-tet include those described in U.S. Pat. Nos. 3,538,100; 3,186,994; 4,225,718 and 4,256,894. Sym-tet is produced according to U.S. Pat. No. 3,186,994 by chlorinating, in the absence of a catalyst, a polychloro-.alpha.-(trichloromethyl)pyridine in the liquid or gas phase. According to U.S. Pat. No. 4,256,894, sym-tet is prepared by reacting a chloro substituted .alpha.-(trichloromethyl)pyridine in the liquid state with chlorine at temperatures of at least about 160.degree. C. in the presence of a catalyst.